Commonly used adsorbents in the industry include: silica gel, activated alumina, activated carbon, molecular sieves, etc., as well as adsorbent materials developed for selective adsorption of certain components. The success of gas adsorption separation depends largely on the performance of the adsorbent. Therefore, the choice of adsorbent is the primary problem in determining the adsorption operation.
Silica gel
Silica gel is a hard, amorphous chain-like and network-like silicic acid polymer particle with a molecular formula of SiO2.
nH2O is a hydrophilic polar adsorbent. It is an aqueous solution of sodium silicate treated with sulfuric acid to form a gel, which is washed with water to remove sodium sulfate and dried to obtain a glassy silica gel which is mainly used for drying, gas mixture and separation of petroleum components. Industrially used silica gel is divided into two types: coarse pores and fine pores. The coarse pore silica gel can absorb more than 80% of the weight of the adsorbent under the condition of relative humidity saturation, and under low humidity conditions, the adsorption amount is much lower than that of the fine pore silica gel.
Alumina
Activated alumina is made by heating and dehydrating aluminum hydrate. Its properties depend on the structural state of the initial hydroxide. Generally, it is not pure Al2O3, but a partially hydrated amorphous porous structure material, which is not only amorphous. The gel, as well as the crystals of hydroxide. Activated alumina is also known as its capillary channel surface with high activity.
It has a strong affinity for water and is an adsorbent for deep drying of trace water. Under certain operating conditions, it can be dried to a depth of -70 ° C below the dew point.
Activated carbon
Activated carbon is made by carbonizing and activating carbonaceous materials such as charcoal, nut shell and coal. Activation methods can be divided into two broad categories, namely, drug activation methods and gas activation methods. In the drug activation method, a chemical such as zinc chloride or potassium sulfide is added to the raw material, and carbonization and activation are carried out by heating in an inert atmosphere.
The gas activation method is to heat the activated carbon raw material in an inert atmosphere, usually after removing volatile components at 700 ° C or lower, and then introducing steam, carbon dioxide, flue gas, air, etc., and reacting at a temperature of 700 to 1200 ° C. Its activation. Activated carbon contains many capillary pore structures and therefore has excellent adsorption capacity. Therefore, it is used in various aspects such as water treatment, decolorization, and gas adsorption.
